A plant absorbs CO2 and performs photosynthesis. Therefore, in general, a photosynthesis rate of the plant is measured on the basis of CO2 concentration under an environment in which the measurement target plant is present (e.g., Patent Literature 1).
An apparatus and a method for measurement of a photosynthesis rate in the prior art are shown in FIG. 10. The air is introduced into an introduction line 82 by a pump 81 and, after passing the filter 80, sent to a flow-rate control section 83. The flow-rate control section 83 feeds a constant percentage (e.g., 75%) of the air into a sample line 84 as a sample gas and feeds the remaining (25%) air into a reference line 85 as a reference gas at a constant rate.
The sample gas passes through a flow meter 86, a chamber 87, and a gas analyzer 88 in order. In the chamber 87, light is radiated from a light source on a leaf L serving as a measurement target (hereinafter referred to as measurement leaf). The measurement leaf L absorbs CO2 of the sample gas in the chamber 87 and performs photosynthesis. CO2 concentration reduced by the photosynthesis is measured by the gas analyzer 88 downstream of the chamber 87.
In the reference line 85, the reference gas passes through a gas analyzer 89. At that time, CO2 concentration of the reference gas is measured by the gas analyzer 89.
A difference between the CO2 concentration of the reference gas and the CO2 concentration of the sample gas is calculated. A photosynthesis rate is obtained by multiplying the difference with a flow rate of the sample gas measured by the flow meter 86.